package com.sinai.mshab.format.util;

/**
 * This interface contains almost all the methods that the {@code
 * java.util.Observable} class has, except it is an interface. There are a
 * number of times when a class has to extend some other class and is thus
 * unable to be {@code Observable}. Furthermore, it is not possible to make
 * interfaces {@code Observable} and thus insure all the concrete classes are
 * also {@code Observable}. Therefore, this interface had to be created.
 * 
 * @author Arthur Kalmenson
 * @author Sergey Vesselov
 */
public interface Observable {

	/**
	 * Adds a new {@link Observer} to observe this object.
	 * 
	 * @param observer
	 *            the new observer
	 */
	public void addObserver(Observer observer);

	/**
	 * Returns the number of {@link Observer}s this object has.
	 * 
	 * @return the number of {@code Observer}s this object has.
	 */
	public int countObservers();

	/**
	 * Removes the {@link Observer}, {@code observer}, from the list of
	 * observing objects.
	 * 
	 * @param observer
	 *            the {@code Observer} to remove.
	 */
	public void deleteObserver(Observer observer);

	/**
	 * Deletes all the {@link Observer}s this object has.
	 */
	public void deleteObservers();

	/**
	 * Notifies all {@link Observer}s that this object has now changed.
	 */
	public void notifyObservers();

}
